build(deps): bump PowerShell to 7.6.5

[JamieMagee]

What are you trying to accomplish?

Update PowerShell from 7.4.5 to 7.6.5, the current stable release. This intentionally moves the NuGet image beyond the 7.4 LTS line.

Anything you want to highlight for special attention from reviewers?

The existing architecture mapping is unchanged: Docker amd64 downloads the PowerShell x64 asset, while arm64 downloads the arm64 asset. The major-version install path, /usr/bin/pwsh symlink, .NET SDK versions, and libssl packages are also unchanged.

Local BuildKit downloads hit TLS EOF errors without a validation-only proxy. An unchanged 7.4.5 control build failed in the same way, while a normal container downloaded 7.6.5 successfully. The non-interactive bin/test command also needed a pseudo-TTY because the development container enables TTY attachment.

How will you know you've accomplished your goal?

The NuGet image build downloaded powershell-7.6.5-linux-x64.tar.gz, reported PowerShell 7.6.5, installed the targeting packs, and exported ghcr.io/dependabot/dependabot-updater-nuget:latest.

The built image reports PowerShell 7.6.5. All PowerShell assertions passed, as did the C# test groups containing 14, 3, 10, 77, 37, and 879 tests.

All required CI checks pass.

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused version update was validated successfully with no unresolved issues.

Review tier: Balanced
Findings: None

What changed in this PR

Updates the NuGet updater image from PowerShell 7.4.5 to 7.6.5.

Changes:

• Bumps the default PowerShell version while preserving existing architecture and installation logic.

File	Description
nuget/​Dockerfile	Updates the PowerShell version pin to 7.6.5.

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